planet

(round object orbiting a star that clears out its own orbital path)

The term planet is used for major objects orbiting stars
other than binary-star companions.
Detected extra-solar planets are so-far sufficiently large that there
is no need to consider whether they qualify as "major".
For the solar system, the IAU distinction is that the object be
sufficiently massive that gravity draws it into a spherical shape
and also massive enough to dynamically clear any planetesimals
out of the path of its own orbit.
This latter distinction (termed clearing the neighborhood)
distinguishes it from a dwarf planet, and is what disqualified Pluto
from being a "normal planet"
(and incidentally disqualifies Ceres, once a "planet" as well),
leaving the solar system with eight known planets out of the hundreds
of thousands of objects known to orbit the Sun.

The object must also not be so massive as to trigger
fusion and thus qualify as a star.
The IAU considers an object above 13 Jupiter-masses to be a
brown dwarf companion, that mass being an adopted estimate
of the mass that could trigger deuterium-fusion.